1. Field of the Invention
The present invention relates to a sheet shaped optical element package, a method of use of sheet shaped optical elements, a method of manufacturing a sheet shaped optical element package, and a device for manufacturing a sheet shaped optical element package. The sheet shaped optical element package of the present invention is a package structure in which sheet shaped optical elements are supported by a base or a protection film or the like. The sheet shaped optical element package can be delivered in the form of such a package structure.
2. Description of the Prior Art
Optical elements constructed in the shape of a sheet, which have been used for various purposes, are known. For instance, a lens known as a fresnel lens is made in the shape of a film. Also, a so called prism sheet, that is, a prism made in the shape of a sheet, is known. Also a micro lens in a shape of a sheet is known.
In the prior art, sheet shaped optical elements are used, for example, as a display of a mobile phone, and as a display of a digital camera FIG. 8 shows a schematic view of the construction of a lightning system called back light system As shown in the figure, the light from a light source 4 is reflected by a reflector sheet 5 located in the back position, and goes through a light guide 6, which can introduce the light. After that, the light is diffused by a diffuser 7, and goes through a back side prism sheet (longitudinal) 1b and a surface side prism sheet (latitudinal) 1a, and finally illuminates a liquid crystal display. In the instance shown by the figure, two sheet shaped prisms are used as optical elements; one is positioned on the surface side and the other is positioned on the back side. The reason for using such two sheet shaped prisms is described below. As each of the sheet shaped prisms has a directional function, the brightness of the light introduced through each prism is enhanced in the different directions. Therefore, by the use of the two sheet shaped prisms, the illumination efficiency is advanced. For example, Japanese patent application laid open publication No. Heisei 5-203950 (203950/1993) discloses the structure described below. The structure has plural sheets, and one side of each of the plural sheets has many prisms, each of which is triangular in sectional view. On each of the plural sheets, the edges (ridges) of the triangles are arranged in a parallel series. In the structure, the plural sheets are piled in such a manner that the edges (ridges) of the triangles form an angle of 5-˜85—with each other. By the use of such structure, the prism system clearly illuminates the LED.
Especially, in the structure in which the light source is positioned at the edge of the display as shown in FIG. 8, the construction of the sheet shaped optical element is of prime importance, in order to introduce the light to the center of the display, or to introduce the light to the surface of the display equally. The light source cannot always be located at a suitable position to obtain the desired illumination on the display. The form of the light source can be varied, for example, a point source or a line source. Therefore, it is necessary to introduce the light suitably by the sheet shaped optical element, in order to give the proper light distribution on the display.
The aforesaid prior construction shown in FIG. 8 is an example of a back light system, in which a light source is located on the back side of the display to be illuminated. Another prior construction has been used also, as front light system in which a light source is located on the front side of the display. In the front type construction, a light source 4 is located on the surface side of the display.
The above mentioned layer system is one example of the structures of the sheet shaped optical elements. Other structures can be applied. For example, the structure can comprise only three elements; that is, one is a prism sheet, which is preferably rich in light direction effects and in light collecting effects, another one is a light guide, and the other one is a reflector. A structure comprising only two sheets of prisms and a reflector can be used. Any other structure can be used. According to the necessity, the manner of assembling the sheet shaped optical elements, and how to use them can be determined variously by the users.
When such sheet shaped optical elements are conveyed to users, or they are transferred for processing, the sheet shaped optical elements are, in general, packaged and supported by guard materials. The sheet shaped optical elements have recently become thinner and smaller in size. Therefore, the package structure is of great importance now. It is also desired to package the sheet shaped optical elements so as to treat them easily when they are processed after being transferred, especially when they are picked up to be processed. In addition, as described above, the manner of constructing sheet shaped optical elements and what systems use them are varied. Namely, various forms are required in accordance with various demands.
The kind of sheet shaped optical element package as above mentioned, the construction of which is shown in FIG. 9 (plan view) and FIG. 10 (section view), has been generally accepted. This construction consists of small sheet shaped optical elements 1, for example, lens films which are lenses each made in the shape of a sheet, or a prism sheet which is a sheet shaped optical element with prism ability, each optical element being covered by a cover film 31 of equal size. The reason why the equally sized cover film is used is because the optical element 1 and the cover film 31 are cut at the same time when they are obtained. The base film 2 serves to support the sheet of the optical element 1 with the cover film 31. At the same time, the base film serves as a protection sheet.
In the prior art, the above mentioned sheet shaped optical element package is formed in a shape corresponding to the shape of the display surface as shown in the figure, for example rectangular, as in FIG. 9. Each sheet shaped optical element is slantingly arranged on the base film 2 as shown in FIG. 9. In other words, a side of each sheet shaped optical element, for example a longer side of each sheet shaped optical element, forms a certain angle with the longer side of the base film 2. The reason is that the specifications of the machines of the users are different from each other. For instance, an angle of 5°, or an angle of 13° may be employed. (Refer to Japanese patent application laid open publication No. Heisei 5-203950 (203950/1993) mentioned above).
The reason why the optical element 1 has the oblique position mentioned above, is as follows. It is necessary to give the certain specific direction of refraction to the light from the light source, like the back light. When the light illuminates the display such as a liquid crystal display of a mobile phone, it sometimes occurs that a striped vision appears on the display. This phenomenon is caused by “Moire which is an inequality of the brightness on the surface of the display. The inequality of the brightness occurs by the interference generated when the refracted light, introduced in its direction determined by the sheet shaped optical element 1, goes through the picture elements (dots) of the liquid crystal cell. The degree of the interference is determined by the size of the picture elements (dots) of the liquid crystal cell, and the angle of incidence for the refracted light. Therefore, the oir can disappear through the control of either the size or the angle. Generally speaking, as the size of the picture elements (dots) of the liquid crystal cell is determined by the resolution of the display, it is considered necessary to give a certain angle to the sheet shaped optical element, such as a prism sheet, in order to prevent the appearance of the oir pattern. In this case, the angle must be given differently according to the size of the picture elements of the liquid crystal cell. As mentioned above, since it is desired to illuminate the surface of the display equally, in order to reduce the oir pattern to a minimum, the sheet shaped optical element 1, such as a prism sheet, must be given a certain angle in the prior art.
The sheet shaped optical element is generally produced by cutting off a sheet, or stamping out a sheet from a wide sheet of the material. The material sheet is usually designed that it refracts the light perpendicularly. Therefore, by giving a certain angle to the sheet of the material when it is cut, it is possible to provide the optical direction to the sheet shaped optical element 1. In the prior art, each sheet shaped optical elements 1 is put on the base film as it is, namely, it makes an angle with the base film. Consequently, they are arranged slantingly as shown FIG. 9.
The prior known art described above have difficulties as explained below.
1) They are not suitable for automation, because the products are delivered in a sheet state in which sheet shaped optical elements are arranged in length and breadth.
2) As the size of the cover film 31 is equal to that of the sheet shaped optical element, it is not easy to separate them from each other.
3) When they are used in a liquid crystal display system as mentioned above, as a nature of the products, namely in order to prevent the interference with the liquid crystal display, a certain angle must be given between the four sides of the base film 4 and the four sides of the sheet shaped optical element. The angle is, for example, 5° or 13°, but the value of the angle can be varied according to the desired specification of the products. Consequently, the direction of the base film 4 is different from that of the sheet shaped optical element. As a result, it is difficult to treat the products. It is also difficult to pick up the sheet shaped optical elements in order to process them.
4) As the sheet shaped optical elements are arranged in length and breadth, a rather wide space is necessary to keep and stock them. Recently, manufacturing lines have changed from conveyer systems to cell (one person) systems. Therefore, such necessity for large storage space causes much inconvenience.